1. Field of the Invention
The present invention relates generally to moving substrates between processing chambers, and more specifically, to a method and system for transporting a plurality of substrates between a transfer chamber and at least one processing chamber.
2. Discussion of the Background
Commercial wafer processing systems are very expensive. Many wafer processing systems process a wafer by (1) transferring a wafer from a wafer cassette to a processing chamber, (2) processing the wafer, (3) returning the wafer to the cassette, and repeating steps (1)–(3). In the field of wafer processing, overhead time is time the processing chamber does not spend processing wafers (e.g., the time utilized to transport a substrate from a cassette to a processing chamber and back after completion of the processing steps). The more overhead time, the less “throughput” a system will be capable of achieving. In other words, the more time the processing chamber remains idle, the lower the total number of substrates that will be processed within a given time period.
In general, the overall cost of processing a wafer substrate is most influenced by two factors, i.e., (1) the throughput of the system and (2) the cost to purchase or build the system. In order to reduce the overall cost of processing a wafer, those factors must be optimized. As a result, system users attempt to recoup their investment in the cost of the system by processing as many wafers per system per day as possible. In many processes, however, overhead steps (e.g., transferring the substrate from the cassette to the processing chuck, clamping the substrate to the processing chuck, testing the clamping of the substrate in the processing chuck, performing any pre-processing steps, and transferring the processing chuck to the processing chamber) require a significant period of time during which the processing chamber is inactive. Therefore, a system is needed that increases the throughput of a wafer processing system by reducing the amount of time the processing chamber is inactive.
The industry continually pushes to decrease cost of processing wafers. Without complete shifts in the methods wafers are processed, each new generation of equipment is required to be more capable thus increasing equipment cost. The equipment designer can only increase throughput to make significant changes in processing cost.